This invention is concerned with mould mechanisms for glassware forming machines.
Mould mechanisms for glassware forming machines normally comprise a first mould support arranged to support one or more mould portions, a second mould support arranged to support the same number of mould portions and mould operating mechanism arranged to move the mould supports between a mould closed position, in which the mould portions on one support engage the mould portions on the other support to define mould cavities into which molten glass can be moulded, and a mould open position in which the mould portions are separated to allow moulded glass to be removed from the cavities.
Such mould mechanisms are commonly used in glassware forming machines of the I.S. type, that is to say a machine which comprises a plurality of sections each of which operates to mould gobs of molten glass into glass containers. The sections are arranged to receive gobs from a common source and operate cyclically with phase differences between the various sections. Each section comprises a blank station at which gobs are moulded to an intermediate shape or parison, and a finish station at which parisons are moulded into complete containers. A section has a mould mechanism as described above at its blank station to provide mould cavities in which the parisons are moulded, and at its finish station to provide mould cavities in which the complete containers are moulded.
In many I.S. machines the mould mechanism comprises mould supports which are provided by arms pivotally mounted on a common vertical pivot, but in others, generally known as the A.I.S. type of machine, the mould mechanism comprises mould supports which are linearly movable towards and away from each other. The mould supports may each support mould portions which cooperate to provide one, two, three or four mould cavities.
In the moulding operations considerable forces are applied to the molten glass to form it into the required shape, and these forces tend to force the mould portions away from each other, thus to separate the mould portions slightly and to cause the formation of seams on the moulded glass. Further at certain stages in the moulding operation downward forces are applied to the mould portions, which may cause deflection of the mould portions and again result in opposed mould portions not being in perfect correspondence or contact, again to result in the formation of faults on the moulded glass.
Various solutions have been suggested to avoid distorting movement of the mould portions. In UK Patent Specification No. 2194784 is described a mould mechanism for a glassware forming machine comprising transversely extending shafts, first and second opposed mould supports each having first end portions mounted on said shafts for linear movement between mould closed and mould open positions, mould operating mechanism arranged to move the mould supports between mould closed and mould open positions and acting on said first end portion and first and second clamping devices arranged to hold the first and second mould supports in their mould closed positions. However, this mould mechanism is not completely successful in solving the problem. Firstly, the mould operating mechanism comprises a pneumatic cylinder linked to the mould supports by a system of pivoted levers. The mould closing force has to be transmitted to the mould supports through a shaft, and there is a possibility of torsional deflection of this shaft, thus effectively to reduce the force with which the mould members are held closed. Further a system of links is inherently subject to cross forces which cause distortion and result in wear, particularly of the transversely extending shafts and of the portions of the mould supports sliding on them. Such wear can give rise to small undesirable deflections of the mould supports. Further still, there is a tendency to wish to use increasing numbers of mould cavities in any one section of the glassware moulding machine--whereas at one time one or two cavities per section were usual, today three or even four are common. The increase in the number of cavities increases the possibility of deflection of the mould support members. While the mechanism described in UK No. 2194784 comprises clamping devices to hold the mould supports in their mould closed positions, these operate on central portions of the mould and are themselves necessarily capable of distortion unless made excessively robust.
It is one of the objects of the present invention to provide a mould mechanism for a glass forming machine in which distortion or movement of the mould supports when in their mould closed position is minimized.